Hi Christophe,

On Fri, Sep 22, 2023 at 10:32:46AM +0000, Christophe Leroy wrote:

Hi Mike,

Le 18/09/2023 à 09:29, Mike Rapoport a écrit :

quoted

From: "Mike Rapoport (IBM)" <rppt@kernel.org>

powerpc overrides kprobes::alloc_insn_page() to remove writable
permissions when STRICT_MODULE_RWX is on.

Add definition of EXECMEM_KRPOBES to execmem_params to allow using the
generic kprobes::alloc_insn_page() with the desired permissions.

As powerpc uses breakpoint instructions to inject kprobes, it does not
need to constrain kprobe allocations to the modules area and can use the
entire vmalloc address space.

I don't understand what you mean here. Does it mean kprobe allocation 
doesn't need to be executable ? I don't think so based on the pgprot you 
set.

On powerpc book3s/32, vmalloc space is not executable. Only modules 
space is executable. X/NX cannot be set on a per page basis, it can only 
be set on a 256 Mbytes segment basis.

See commit c49643319715 ("powerpc/32s: Only leave NX unset on segments 
used for modules") and 6ca055322da8 ("powerpc/32s: Use dedicated segment 
for modules with STRICT_KERNEL_RWX") and 7bee31ad8e2f ("powerpc/32s: Fix 
is_module_segment() when MODULES_VADDR is defined").

So if your intention is still to have an executable kprobes, then you 
can't use vmalloc address space.

Right, and I've fixed the KPROBES range to uses the same range as MODULES.
The commit message is stale and I need to update it.
 

Christophe

quoted

Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
---
  arch/powerpc/kernel/kprobes.c | 14 --------------
  arch/powerpc/kernel/module.c  | 11 +++++++++++
  2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 62228c7072a2..14c5ddec3056 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c

@@ -126,20 +126,6 @@ kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offse
  	return (kprobe_opcode_t *)(addr + offset);
  }
  
-void *alloc_insn_page(void)
-{
-	void *page;
-
-	page = execmem_text_alloc(EXECMEM_KPROBES, PAGE_SIZE);
-	if (!page)
-		return NULL;
-
-	if (strict_module_rwx_enabled())
-		set_memory_rox((unsigned long)page, 1);
-
-	return page;
-}
-
  int arch_prepare_kprobe(struct kprobe *p)
  {
  	int ret = 0;

diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
index 824d9541a310..bf2c62aef628 100644
--- a/arch/powerpc/kernel/module.c
+++ b/arch/powerpc/kernel/module.c

@@ -95,6 +95,9 @@ static struct execmem_params execmem_params __ro_after_init = {
  		[EXECMEM_DEFAULT] = {
  			.alignment = 1,
  		},
+		[EXECMEM_KPROBES] = {
+			.alignment = 1,
+		},
  		[EXECMEM_MODULE_DATA] = {
  			.alignment = 1,
  		},

@@ -135,5 +138,13 @@ struct execmem_params __init *execmem_arch_params(void)
  
  	range->pgprot = prot;
  
+	execmem_params.ranges[EXECMEM_KPROBES].start = VMALLOC_START;
+	execmem_params.ranges[EXECMEM_KPROBES].start = VMALLOC_END;
+
+	if (strict_module_rwx_enabled())
+		execmem_params.ranges[EXECMEM_KPROBES].pgprot = PAGE_KERNEL_ROX;
+	else
+		execmem_params.ranges[EXECMEM_KPROBES].pgprot = PAGE_KERNEL_EXEC;
+
  	return &execmem_params;
  }

-- 
Sincerely yours,
Mike.